The fuel check is more of a pre flight belt and braces check to confirm what the gauges are saying even the optical ones can get blocked with crap. It needs as folk have been saying to be able to look in the tank and see calibration marks a bit like the cross in the tommy tank to gauge how much you have. None off this poking ****ty sticks into it and then hoping who ever made the stick up got it right. Apart from anything else you end up with a impregnated with petrol fire hazard on the plane never mind running the risk of contaminating the tank.
The access thing may seem daft to the majority of PPL's but when you have a full range of mobility of punters turning up it can make a huge difference to how much aof PIA it is getting them loaded. The tommy/PA28 with the help of a carvan step is great nice wide walk way, door frame to grab onto. Then once they are next to the door they have a small lip to get there leg over before going down. To be honest you would be better talking to the disabled flying club. The PA38 is a bit to much of a step down, the PA28 is better but its suffers the problem that they have to shuffle there backside over once they are in. The cessna's its becomes more intimate with hands on bottoms and hefty shoves to get them loaded. Best way again is a step then get them to sit backwards then swivel round in the C172 but The C150/C150's the seat doesn't go back far enough and your head is banging off the wing.
On the matter of bits to grab you need good solid obvious grab points. If its in front of the punter they will grab it and put thier full weight on it. If you have designed something that is grabbable but you haven't designed it to have a 110kg bloke pulling on it its only a matter of time before it gets broken.
Not to bothered about having more than two doors on the 4 seater three would be nice. But you definately need a two seater option. No point taking an extra two seats of weight with you for 80% of of your flying.
Pitch trimmer
under carrage you have it with no spats or any of that crap and a jacking point thats works with a car jack. And if possibly even a tempory get it off the runway attachment point for a castor. And the nose gear needs to be a meaty job with good prop clearance when flat and that flat tyre and when the seals have gone on the gas combined.
PTT
pain in the backside getting them fixed. Sacraffical socket would be a better way of putting it with the PTT modual swappable without resorting to using any tools apart from maybe a philips to release the modual. The modual so shaped it can only go in one way.
Tail
Full harness for depature and landing but allows you to disconnect the shoulders in the air to get to the back etc.